// is a minimal "echo" server.
package main

import (
	"image"
	"image/color"
	"image/gif"
	"io"
	"log"
	"math"
	"math/rand/v2"
	"net/http"
	"strconv"
	"strings"
)

func main() {
	http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
		q := strings.Split(r.URL.RawQuery, "=")
		cycles, _ := strconv.Atoi(q[1])
		lissajous(w, float64(cycles))
	})
	log.Fatal(http.ListenAndServe(":8000", nil))
}

// func handle(w http.ResponseWriter, r *http.Request) {
// 	fmt.Fprintf(w, "%s %s %s\n", r.Method, r.URL, r.Proto)
// 	for k, v := range r.Header {
// 		fmt.Fprintf(w, "Header[%q] = %q\n", k, v)
// 	}
// 	fmt.Fprintf(w, "Host = %q\n", r.Host)
// 	fmt.Fprintf(w, "RemoteAddr = %q\n", r.RemoteAddr)
// 	if err := r.ParseForm(); err != nil {
// 		log.Printf("%v", err)
// 	}
// 	for k, v := range r.Form {
// 		fmt.Fprintf(w, "Form[%q] = %q\n", k, v)
// 	}
// }

var palette = []color.Color{color.White, color.RGBA{255, 0, 0, 255}, color.RGBA{0, 255, 0, 255}, color.RGBA{0, 0, 255, 255}}

const (
	whiteIndex = 0 // first color in palette
	blackIndex = 1
)

func lissajous(out io.Writer, cycles float64) {
	const (
		res     = 0.001
		size    = 100
		nframes = 64
		delay   = 8
	)
	freq := rand.Float64() * 3.0
	anim := gif.GIF{LoopCount: nframes}
	phase := 0.0
	for i := 0; i < nframes; i++ {
		rect := image.Rect(0, 0, 2*size+1, 2*size+1)
		img := image.NewPaletted(rect, palette)
		for t := 0.0; t < cycles*2*math.Pi; t += res {
			x := math.Sin(t)
			y := math.Sin(t*freq + phase)
			index := i%3 + 1
			img.SetColorIndex(size+int(x*size+0.5), size+int(y*size+0.5), uint8(index))
		}
		phase += 0.1
		anim.Delay = append(anim.Delay, delay)
		anim.Image = append(anim.Image, img)
	}
	gif.EncodeAll(out, &anim)
}
